Dibenzoxacarbocyanines and process of preparing them



-l' rays of the spectrum; it is necessary to treat the Patented Dec. 12.1933

DIBENZOXACARBOCYANINES AND PROCESS OF PREPARING THEM Leslie G. S. Brooker, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New York No Drawing. Application February 20, 1932 Serial No. 594,380

16 Claims. (01. 260-44) This invention relates to new chemical c0m-. Bottcher (Ber., 1883, 16,1933). Asomewhatdifpounds and more particularly to a new class of ferent method of preparing this base was later photographic sensitizing dyes known as didescribed'by Michel & Grandmougin (Ben, 1892, benzoxacarbocyanines, and methods for their 25, 3429). The structure'ofthe 2-methyl-flpreparation. naphthoxazole is as follows: 55

It has been known for'some time in the photographic art that in order to render photographic emulsions, such as gelatino-silver-halide emulsions, sensitive to substantially all of the visible 60 emulsions, either by overcoating or by admixture with theemulsions' themselves, with a com pound which extends or enhances the sensitivity of the emulsions to light beyond their natural .15 sensitivity. Many dyes suitablefor this purpose have been previously described in the literature; such for instance as pseudocyanine, 'sensitol red, krYPmc-Yaninei F m fl f r and ,F hg The numbering'given is thatiused in' Richters Additional 'ones have also {been described him e m t fi' Vrbindungen and previously med qf d j applications. 'f l' also in Chemical Abstracts The i-methyl-e- 7 0 instanqe n q r nin es r ed naphthoxazole'may be preparedffrom 2-aminoin my Patent'Nor 1,846,30 a e 3 2 l-nlphthdl in a mannersirnilar to that described and mapplica ion semlN 4 ;1 5, by' Michel and Grandmou'gin (10c. cit.) for the 12, 1930. The dibenzoxacarbocyanines described isomefic g t y1 hth az l 25 in the instant application were likewiseldespribed This base will yield dibenzoxacarbocyanine in therabove mentioned p te t which i dyes, the formation of which probably takes related K instead of employing a place as follows: first, the-base is converted into P hQ mW n material-9f" ajf suitable alkyl quaternary salt, such as the Producing the; t d b o o a oc an one inethoeor ethb-p-tdluefiesulfonateor the methio- 30 could replace the Su p the thiaZOIB y dide or ethiodide, by heating the base .with a oxygen. and produce a dibenzoxacarbocyanine by suitable substanceisuch as methyl p-toluenesul using the Tmethylnaphthoxazole as. the starting f onat'e or methyl iodide under appropriate condimaterial. These.Tdibe'nzoxacarbocyanines sensi: tions, for instance. tize a gelatino-silverqhalide emulsion containng q v r j 35 them to the yellow-green portion of the spec- I 1.

trum, contributing a maximum sensitivity at-gapproximately 55 50 Angstrom units, 1

t It isan object of; this inventionQtherefore; to

provide a new class of sensitizing dyes for photo,

40 graphic emulsions, and further to'provide a process by which those dyes may be readily prepared. It is'a specific object of this inv'entionto Q t r Prepare dibenzoxacarbocyanines and to proap ra e' t -fl p qg 45 vide a method for' their preparationf Other ob-' i a f jects will occur to those skilled in theartupon t p a further pe a of this specification" 1 where R is an alkyl group such as methyl or e CO P d known a y -fip ethyl, and X is"a'suitable acidic radical, such as thoxazole, for instance,.was first described, top-toluenesulfonate or iodide. 50 gether with its 'methodfof' preparation by This quaternarysalt, for instance, 2-methyl-pnaphthoxazole metho-para-toluenesulfonate (2 but merely illustrating the manner of effecting the mols.) is then heated with ethyl orthoformate (1 mol.) in the presence of anhydrous pyridine whereupon the dye is formed. The reaction may be represented as follows:

broad principles of my invention.

Example I .-2 :2'-dimethyl-3 :4 :3 :4'-dibenzoxacarbocyam'ne bromide -orn+mo-o-om+mc- 01% N R x g 2-meth LB-naphthoxazole ethyl pyridine alky quaternary salt orthoformate 5 ox /o 4, CH=OHCH=C 1 +3EtOH+L I 2' 2 3 N/ /N\ N it v R x dibenzoxacarbocynine salt In practice a better yield of dye is obtained it an excess of ethyl orthoformate is employed over that theoretically necessary. Other ortho-esters of formic acid, such as trimethyl orthoformate, may, of course, be used. It is desirable to number the dye molecule in the above fashion in order that this numbering will be in accord with that given to the sulphur containing dye named, for instance, in the above mentioned patent. The final namefor a dye of this typetherefore becomes 2,2'-dialkyl-3:4:3' :4'-dibenzoxacarbocyanine salt. In the above formulae, R. may besimilar or dissimilar alkyl'radicals depending upon whether the naphthoxazole quaternary saltcontains only the one alkyl radical or whether two portions 01' the salt are employed eachhaving a difierent alkyl radical. g

After the formation of the dye, it may be isolatedand purified by ordinary chemical methods; or'it maybe converted into another salt, usually a less soluble one, by double decomposition in the ordinary fashion. For instance the p-toluenesulfonate of a dye may be converted into a bro mide by treatment, in solutiomwith a soluble bromide, such as'sodium bromide; The acid radical finally employed may be one such as a halide, perchlorate, nitrate, acetate, p-toluenesulfonate or in fact any salt forming acid radical which will not greatly decrease or destroy the sensitizing properties of the dye. V X in the above formulae of the carbocyanines may represent any of these acid radicals.

In the dyes the two naphthoxazole nuclei are linked together by a chain comprising three carbon atoms. Since the :CH- group is called the methenyl group, the chain =CH--CH=CH may be called a trimethenyl chain. Cyanine dyes containing this trimethenyl chain are commonly called carbocyanine dyes.

, Examples of specific methods by which these dyes may be'prepared areas follows, but it will of course be understood that these are not limiting 6.1 g. 2-methyl-5-naphthoxazole is heated with 6.2 g. methyl p-toluenesulfonate for 6 hours at about 160 C., 'Duringa further 15 hours heating at 130-140" C. the product solidifies to abrownish solid. The product, substantially Z-methylfi-naphthoxazole metho-p-toluenesulfonate, is boiled under reflux with anhydrous pyridine (40 cc.) and ethyl orthoformate (5.5 00., 100% excess) A reddish orange color forms rapidly and refluxing is continued ior 45 minutes. A hot solution of excess of potassium bromide (20 g.) in water (100 cc.) is added to the reaction mix ture, and the dye is rapidly precipitated as the bromide. The crude dye may be freed from impurities by boiling itsucoessively with water and then with acetone, and then recrystallizing it from methyl alcohol, whereupon it is obtained as a mass of red silky needles which 'give an orange-solution in the solvent.

Example II.-Z:2'-diethyl-3.f4:3:4-dibenzo:ra-

- carbocyanine brmnide is refluxed for 45 minutes 'with anhydrous pyridine (30 cc.) and ethylorthciormate (8.2 cc,

100% excess). The dye is then precipitated as the bromide by adding an excess of a warm solution of potassium bromide (20 g.) in water (100 00.). After filtering, the dye may be washed with water and then with hot acetone and finally recrystallized from methyl alcohol, in which it gives an orange solution. It is obtained as red dish needles.

In the same manner that the 3:4:3z4' diben zoxacarbocyanine is prepared; one .inay prepare the 516-15 16f .dibenzoxa'c'arbocyanine, if :one were to start with the .1 methyl+alpha-naphthoxazole instead of the 2-methyl-p5naphthoxazole as above 5 described. =The structure .of the bas'eis-given below; as wellas that of anoxacarbocyanine dye derived fromit.-.. l a Q 2, 2 -dialky l- 5 r625" 6dibenzoxacarbocyanine salt.

The numbering is thatused inmy application where the corresponding sulfur-containing compoundswere used,- namely No.'33'7,177.-

Since the preparation of lrmethyl-a-naphthoxazole is not described in the literatureit. will be given hera a ,Z-nitr -I-naphthoI is first prepared; (see, for instance,I-Iodgson 8: Kilner, J C. S. 1924, 125, 807). This compound is'then reduced to the corresponding .2-amino-1-naphthol, using tin and hydrochloric acid as recommended by Lieber-.

mann & Dittler (Ben, 1874; 7, 240; Liebermann, Ann, 1876, 183, 246). The hydrochloride of the base is then heated with acetic acid and sodium acetate for several hours in a similar fashion to that prescribed for the preparation of 2-methyl- B-naphthoxazole by Michel & Grandmougin (Ben, 1892, 25, 3429). The excess of acetic acid is then slowly. distilled off and the residue is finally distilled in vacuum, using an oil bath to heat the reaction flask. The base distills over and is purified by dissolving the distillate in ligroin, allowing a solid impurity to crystallize out first, and then isolating the base from the mother liquor. The l-methyl-a-naphthoxazole is obtained as a low melting solid.

For the preparation of the dyes the base is converted into a quaternary salt such as the methyl p-toluenesulfonate or the ethiodide in the usual way. The quaternary salt is then condensed with ethyl orthoformate in the presence of anhydrous pyridine as described for the isomeric dyes derived from 2-methyl-p-naphthoxazole.

Example III separate, the p-toluenesulfonate of the dye being very sparingly. soluble in .pyridine, hot or cold. After 30 minutes refluxing, .the reaction mixture is allowed to cool, and the" dye is then filtered offandawashed with cold pyridine and then dried. .The yield isabout 1.3'parts. This dye is 2,2'-dimethyl5 :6:5':6-dibenzoxacarbocyanine p-toluenesulfonate. x

' The dye. may be converted into the bromide by dissolving it in boilingi'methyl alcohol .and add-' ing an excessof an aqueous solution of an alkali bromide, such as. potassium bromide, to the alcoholic solution. The:bromide of. the dye is almost. insoluble'in alcoholic-aqueoussolution in the presence of a large excess of :bromide ions and may be' filtered 01f, washed'with water, and then purified 'by. recrystallization: fromethyl' or methyl alcohol. This dye is calledv methyl- 5: 6:5':.6' -dibenzoxcarbocyanine .bromide. .If

' potassium iodide .is used in Q-place of potassium bromide: then the still less soluble dye iodide is formed.:. The bromide of. the dye crystallizeslfrom'methyl alcohol as a. felted mass of hair-"like crystals, reddish-orange in color. The solution of the dye in the solvent named is orange.

' Example!!! If 1.1. partsof ethyl p-toluenesulfonate are used instead of .the' 1.05 parts ofimethyl p'-toluene-sulfonate are usedin the preceding example, and the two components are heated on the'steam bath for -24 hours, l-methyl-aenaphthoxazole etho-p-toluenesulfonate is produced. This salt iscondensed with ethyl orthoformate in boiling pyridine solution in the same manner described in the preceding example,.using 10 parts of pyridine and 1.6parts of the orthoester. After 30 minutes refluxing the dye is precipitated from the deeply colored solutionby adding thereto an exoess of ,an aqueous solution of potassium iodide. The dyeis filtered ofi, washed with water and with acetone, and is purified by'several recrystallizations from methyl alcohol, in which it gives; .an orange solution. The 2,2'-diethyl- 536:5:6-dibenzoxacarbocyanine iodide is obtained in beautiful garnet-red crystals with a strong blue reflex.

The naphthalene nuclei in both the -methylnaphthoxazoles may be left unsubstituted or they may be substituted.

What I claim is:

1. A process for the preparation of dibenzoxacarbocyanine dyes which comprises condensing two molecular proportions of a ,u-methylnaphthoxazole quaternary salt with one molecular proportion of ethyl orthoformate in the presence of an organic base which is a solvent for the. reactants and which acts to bind acid eliminated from the quaternary salt as a ree sult of the condensation.

2. A process for the preparation of dibenzoxacarbocyanine dyes which-comprises condensing two molecular proportions of a a-methyl-,

naphthoxazole alkyl quaternary salt with one molecular proportion of ethyl orthoformate in the presence of an organic base which is a'solvent for the reactants and which acts to bind acid eliminated from the quatemary salt as a result of the condensation.

3. A process for the preparation of dibenzoxacarbocyanine dyes which comprises condensing two molecular proportions of a 2-methyl-p-.

naphthoxazole alkyl quaternary salt with one molecular proportion of ethyl orthoformate in the presence of an organic base which is a solvent for the reactants and which acts to bind acid eliminates! from the quaternarysalt as a result otthecondensatinn'." r 4'. A process for the preparation of dibenzoxacarbocyanine dyes which comprises condensing two molecular proportions of a mu-methyl naphthoxamle alkyl quaternary salt with one molecular proportion of ethyl orthoiormate in the presence of an' organic base which is a solvent for the reactants and" which acts 'tobindacid eliminated-from the quaternary salt as a result of the condemation-and then converting the con densation product thus formed to 'a ihalidej by double decomposition of the condensation prod uctwithasolublehallde. P w I 5. A processior the-preparation or dibenm'xacarbocyanine dyes whieheomprises condensing two molecular proportions of a 'z-methyl-flnephthoxamle alkyl quatemaryosait with one molecular proportion of ethyl :orthoformate in the presence or! an organic base a:solvent forthe'reactants and which acts to bind acid eliminated from the quaternary salt as a result of the condensation .and then converting the condensation product thus formed to av halide S by double decomposition of the condensation product with a soluble halide.

' l. A processrior the preparation of diben-' aoxacarbocyanine dye: which comprises condensing two molecular. proportions-0t a mumethyl-naphthoxanole alkyi quaternary salt with one'molecular proportionof ethyl orthotormate in the presence oi pyridine.

i '7. A process Iorv the preparation '01- 'dibenmxacarbocyanine dyes which comprises condensing two molecular proportions of a 2 methyl-p-naphthoxazole alkyl quaternary salt with one molecular proportion of ethyl orthoiormate in the presence of pyridine.

8. A process for the preparation of a 2:2-dimethyl 3 24:3: 4' dibenzoxacarbocyanine salt which comprises condensing Z-methyLp-naphthoxaaole metho-p-toluenesulfonate with ethylorthotonnate in the presence of an organic base which is a solvent for the reactants and which acts to. bind acid eliminated from the quaternary salt as a result of the condensation. 9. A process for the preparation of a 2:2'-diethyl-3 :4 3' 4' -'dibenzoxacarbocyanine salt which comprises condensing 2-methyl-fl-naphthoxazole etho-p-toluenesulionate with ethylorthotormate in' the presence 01 an organic base which is a solvent for the reactants and which acts to bind acid eliminated from the quaternary salt as a result of the condensation.

10. A process for the preparation of a 2:2'-dimethyl-3 4 3 z 4' -dibenzoxacarbocyanine halide which comprises condensing Z-methyI-p-naphthoxazole metho-p-toluenesulionate with ethylorthoformate in the presence of an organic base which is a solvent for the reactants and which acts to bind acid eliminated from the quaternary salt as a result of the condensation and then converting the condensation product thus formed to a halide'by double decomposition oi the condensation. product with a soluble halide.

11. A process for the preparation of a 2:2'-diethyl 3:4:3'14' -Idibenzoxacarbocyanine halide which comprises condensing 2-methyl-p-naphthoxazole etho-p-toluenesulionate with ethylorthoiormate in the presence of an organic base which is a solvent for the reactants and which acts to bind acid eliminated from the quaternary salt as'a result of the condensation and then converting the condensation product thus formed to a halide by double decomposition of the condensationproduct with a soluble halide.

12. A dialkyl-dibenzoxacarbocyanine salt.

- 13. A dialkyl-dibenzoxacarbocyanine bromide.

14. A V 2:2'-dialkyl-3:4:3':4'-dibcnaoxacarbocyanine salt.

' 15. 2:2'-dimethyl -3:4:3:4- dibenzoxacarbocyanine bromide.

- 16. 2:2 diethyl 3:4:3:4'-dibenzoxacarbocyanine bromide.

LESLIE G. s. BROOKER. 

